1. Field of the Invention
The present invention relates to a silicon substrate and a silicon substrate manufacturing method, and particularly, to a technique which is preferably used for a silicon substrate having improved gettering performance and provided for manufacturing a thin device such as a memory or a logic device.
Priority is claimed on Japanese Patent Application No. 2008-049847, filed Feb. 29, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
A thin silicon semiconductor device is manufactured by forming a circuit on a silicon substrate sliced from single-crystal silicon pulled in accordance with a czochralski (CZ) method. When impurities such as heavy metal are incorporated in the silicon substrate, device characteristics greatly deteriorate.
A first cause of the incorporation of impurities such as heavy metals in the silicon substrate is metal contamination in a silicon substrate manufacturing process including pulling of a single crystal, slicing, chamfering, and surface processing such as polishing, grinding and etching. A second cause thereof is a heavy-metal contamination in a device manufacturing process including a process of abrading a back face of a wafer to reduce the thickness to about 50 μm after the formation of a circuit on the silicon substrate.
Accordingly, an intrinsic gettering (IG) method of forming oxygen precipitates in a silicon substrate and an extrinsic gettering (EG) method of forming a gettering site such as a backside damage in a back face of a silicon substrate have been used.
Japanese Unexamined Patent Application, First Publication No. 6-338507 discloses a processing technique using the IG method. Japanese Unexamined Patent Application, First Publication No. 2006-313922 discloses an example of the EG method in the paragraph [0005] and a technique related to a carbon ion injection.
As described above, a silicon substrate which is used in a solid-state image sensing device is obtained by the intrinsic gettering method of forming oxygen precipitates by performing a heat treatment for oxygen precipitation before epitaxial growth, or an ion injection method of injecting ions such as carbon ions into a silicon substrate.
In recent years, a device thinning process has been performed and the thicknesses of devices are required to be from 50 μm to 40 μm or less, specifically, about 30 μm. However, heavy-metal contamination mostly occurs particularly in the thinning process as a final device manufacturing process. In the case of the above conventional intrinsic gettering (IG) method, a large portion of an IG layer exhibiting an IG effect is removed in the thinning process if the thickness of the device has been reduced to be in the above range. Therefore, sufficient gettering performance is not exhibited and a problem occurs in that the causes of device malfunction are formed.
In addition, as disclosed in Japanese Unexamined Patent Application, First Publication No. 2006-313922, when a high-temperature heat treatment is performed on a substrate into which carbon is injected, crystal defects (crystal lattice distortion and the like) formed by the carbon injection are reduced and thus there is concern that a function of the defects as gettering sinks deteriorate.
The invention is contrived in view of the above problems, and an object of the invention is to provide a silicon substrate, which has sufficient gettering performance and in which the occurrence of cracking or chipping can be prevented, even when being thinned, thereby improving the yield of the device, and a silicon substrate manufacturing method.